1. Field of the Invention
The present invention relates to a supercharge system of an internal combustion engine having a throttle valve in an intake passageway and particularly to an exhaust bypass valve actuating device of a supercharge system of an engine of this type.
2. Description of the Prior Art
As is well known in the art, a conventional supercharge system (for example, disclosed in a Japenese Patent Application Publication No. 38(1963)-19660) has an exhaust bypass valve actuating device which is controlled in accordance with the pressure in the intake passageway at a location downstream of the throttle valve and the pressure in the intake passageway at a location downstream of the compressor of a turbosupercharge such that the bypass valve opens the exhaust bypass passage so as not to apply the exhaust gas to the turbine of the turbosupercharge thereby preventing a supercharge pressure (the pressure in the intake passageway at the location downstream of the compressor) from exceeding a predetermined value.
However, the bypass valve actuating device has been constructed and controlled such that the bypass valve does not open the bypass passage to apply the exhaust gas to the turbine when the engine is in low load operating condition.
When the exhaust gas is applied to the turbine of a turbosupercharger during any operation of an engine, the back pressure of the engine increases to reduce the power output of the engine. Moreover, when the back pressure increases during a low load operation of the engine, the fuel consumption and the driveability of the engine especially deteriorate. This is for the following reason: When the engine is in such a low load operating condition that the engine produces a small quantity of exhaust gas, the turbine can not produce sufficient power for driving the compressor of the turbosupercharger. Accordingly, the turbosupercharger can hardly perform supercharging to increase the power output of the engine. As a result, a minus effect by an increase in the back pressure is far larger than a plus effect by supercharging to deteriorate the fuel consumption and the driveability of the engine.
Accordingly, when the accelerator pedal is depressed during a low load operation of an engine having the conventional supercharge system, the engine can not produce a sufficient power output. Thus, the conventional supercharge system has suffered from a drawback that the fuel consumption and the driveability of the engine such as the accelerating ability deteriorate.